sort array by date php

usort($array, function($a, $b) {
  return new DateTime($a['datetime']) <=> new DateTime($b['datetime']);
});

<?php
    function compareDate($date1, $date2){
        return strtotime($date1) - strtotime($date2);
    }
    
    $dateArray = array("2021-11-11", "2021-10-10","2021-08-10", "2021-09-08");
    usort($dateArray, "compareDate");
    
    print_r($dateArray);
?>

//Output

Array
(
   [0] => 2021-08-10
   [1] => 2021-09-08
   [2] => 2021-10-10
   [3] => 2021-11-11
)